@plegrand Debian 9 would have to use the php 7 packages. I can assure you that the installer works on a clean installation of Debian 9, but I’ve not tested an upgrade from older Debian 8. If you look in my signature, you’ll see some automated tests centered around the fog installer. All those tests are with 100% clean OSs/installs.

In the past, people who have upgraded their OSs on FOG servers have had mixed success. When it goes right, everything is just peachy. When it goes wrong we spend days - sometimes weeks - helping these people figure out the problems. I’d say it’s been about a 60/40 split, 40 being failure.